Belt type electrolytic grinding machine



Dec. 22, 1964 R. M. BELL 3,152,533

BELT TYPE ELECTROLYTIC GRINDING MACHINE Filed April 17. 1961 RAIVISAY M.BELL AT TO R NEYS United States Patent 3,162,588 BELT TYPE ELECTRGLYTECGRINDING ll IAQHINE Ramsay M. Bell, Schoolcralt, Mich, assignor toHarnmond lsiiachinery Builders, Erica, Kalamazoo, h lich, a corporationof Michigan Filed Apr. 17, 196i, Ser. No. 194,201 1 Claim. ((Il.294-441) This invention relates in general to an electrolytic grindingmachine and, more particularly, to a type thereof having a perforatedbelt and platen through which electrolyte is moved with a minimum ofobstruction so that satisfactory grinding can be performed with aminimum of electrical potential.

This application is a continuation-in-part of my application Serial No.762,163, filed September 19, 1958, and entitled Belt-Type ElectrolyticGrinding Machine, now abandoned.

The use and construction of belt-type grinders have long been familiarand many specific forms have been used. Likewise, the advantages andtechniques involved in removing particles of electrically conductivematerials by electrolytic erosion (often called electro-chemicaldecomposition) are also well established. However, insofar as I amaware, little or no success has been achieved in applying the principl sof electrolytic erosion to the belt-type grinding machine, even thoughit is well known that a belt-type grinder is capable of performingcertain types of grinding operations in a much more efficient andconvenient manner than other types of grinders, such as the disk grinderfor example, particularly because the platen and belt can be formed tofit or otherwise suit cer* tain types of formed workpieces.

Among those obstacles which have apparently impeded the development of abelt-type eletrolytic grinding machine are the proper control and theadequate supply of electrolyte to the grinding zone. Previous attemptsto effect acceptable electrolytic grinding operations with a beltgrinder have required an electrical potential which is so high that itcreates an uncomfortable sensation for the machine operator.

While pursuing this problem, it was found that in order to obtainreasonably satisfactory electrolytic erosion with a belttype grinder,the spacing betwen the anode (workpiece) and the cathode of theapparatus must be eX' tremely uniform and must be held to a very smallvalue, normally under 0.005 inch and preferably about 0.001 of an inch.It was also found that the movement of electrolyte between the cathodeand the anode must have a minimum of obstruction so that there is alwaysan ample supply of electrolyte in the grinding zone. By meeting thisconditions, it is possible and practicable to carry out an electrolyticerosion operation effectively and efiiciently with a voltage supplywhich is low enough to be acceptable to the operator.

Accordingly, a primary object of this invention has been the provisionof an electrolytic grinding machine utilizing a belt-type abrasiveelement.

A further object of this inventionhas been the provision of a belt-typeelectrolytic grinder wherein a sufficiently continuous and adequatesupply of electrolyte can be maintained in the zone between the anodeand cathode of the grinding machine to effect a satisfactory grindingoperation with a sufficiently low electrical potential that it will notproduce uncomfortable sensations for the operator.

A further object of this invention has been the provision of a structurewhereby the basic construction of a non-electrolytic grinding machinecan in the manufacturing operation be modified to provide anelectrolytic grind- 3,l2,58$ Patented Dec. 22, 1964 ing machine withoutmaterially changing such basic construction and without increasing thecost unreasonably by comparison with the cost of a conventionalnon-electrolytic, belt-type grinding machine.

A further object of this invention has been the provision of anelectrolytic, belt-type grinding machine, as aforesaid, which isextremely easy to operate, which requires a minimum of maintenance,which is sturdy and reliable in construction and which performsaccurately.

A further object of this invention has been the provision of aconstruction for a belt-type electrolytic grinder, as aforesaid, whereinthe reach of the belt by which the grinding operation is performed canbe caused to operate on non-linear surfaces of various shapes which maybe convex and/or concave, such nonlinearity being either lengthwise orcrosswise of the belt.

Other objects and purposes of the invention will become apparent topersons familiar with this type of equipment upon reading the followingspecification and examining the accompanying drawings, in which:

FIGURE 1 is a broken, front elevational view of that portion of abelt-type, electrolytic grinding machine embodying the invention.

FIGURE 2 is a broken, fragmentary side elevational view of said grindingmachine.

PXGURE 3 is an enlarged sectional view taken along the line Ill-411 ofFIGURE 1.

FIGURE 4 is a broken sectional view taken along the line IVlV of FIGURE3.

FlGURE 5 is a sectional view taken along the line VV of FIGURE 2 andshowing a modified platen construction.

FIGURE 6 is a sectional view taken along the line VI-VI of FIGURE 5 androtated degrees clockwise.

FIGURE 7 is a fragmentary top view of a modified grinding machineembodying the invention.

For convenience in description, the terms upper, lower and derivativesthereof will have reference to the grinding machine as appearing inFIGURES l and 2, unless otherwise stated to the contrary. The termsinner, outer" and derivatives thereof will have reference to thegeometric center of said grinding machine and parts associatedtherewith. The terms front and rear will have reference, respectively,to the left and right sides of the said machine as appearing in FIGURE2.

The term perforate or derivatives thereof shall be used to describeobjects having a multiplicity of openings therethrougn, regardless ofwhether such openings are formed by a perforating operation or othertype of fcrming operation and the number and size of such openings beingsufficient to permit the electrolyte to flow therethrough at therequired rate.

General Description The ob ects of the invention, including those setforth above, have been met by providing a grinding machine having a pairof spaced and axially parallel rollers around which an endless beltextends, one reach of said belt being, in the embodiment hereillustrated and described, disposed in a substantially vertical planeand having a belt supporting platen adjacent its inner side and a worksupporting table adjacent its outer side. Said belt is in theillustrated embodiment fabricated from an electrically conductivematerial but is in any case a material through which an electrolyte canpass with a minimum of obstruction. Said belt is of uniform thicknessthroughout its length and has an abrasive coating on its outer surfacewhich is electrically nonconductive and is of substantially uniformthickness. The platen has a perforated region which is locatedsubstantially opposite and extends slightly above the work as it facesthe platen. 'l he perforate porner.

. 2) on'its front surface which lies closely adjacent to'and tion ofsaid platen defines one side of an electrolyte chamber which is definedon the remaining sides by the walls of a casing secured to said platen.A device for creating an electrical potential is connected between the.work supporting table and the platen, which are otherwise electrically'insulated from each other. The platen and/or the belt supported thereonserve as a cathode and the workpiece supported upon the table serves asthe anode.

Mechanism including a collecting basinand a pump are provided forreceiving the electrolyte as it moves away from the grinding zone andreturning such electrolyte under pressure to the electrolyte chamber sothat it will pass again through the openings and back into said grindingzone.

Detailed Construction The belt-type electrolytic grinding machine (FIG-URES 1 and 2) is herein selected to illustrate the invention and mayhave a basic construction similar to the belt-type grinder disclosed inpatent application Serial -No. 738,869, filed May 29, 1958, entitledMachine Tool,

and assigned to the assignee of this application, now Patout No.2,900,766. More specifically, the grinding machine 10 is comprised of acentral housing 11 supported upon the upper portion. of a pedestal 12which also supports a driving motor 13 below said housing. An upperpulley 16 is vertically adjustably supported upon the housing 11 and alower pulley 17 is supported upon the shaft 18 of the motor 13 forrotation thereby. The pulleys 16 and 17, which are axially parallel andarranged so thatthe lower pulley 17 is directly under the upper pulley16, are encircled by an endless belt 19 of uniform thickness.

Said belt 19 (FIGURE 3) is in the illustrated embodiment fabricated froman electrically conductive material, such as a strip of woven fabric ofcopper or aluminum. Other materials of non-electrically conductivecharacter, such as fabric, will in certain instances be satisfactory.From whichever material the belt 19 is made, it will have a plurality'ofclosely spaced openings 21 through which an electrolyte can easily pass.These openings should be arranged to cover 'the entire surface of theworkpiece substantially uniformly with electrolyte, but any random orgeometric pattern capable of doing this is acceptable. The

' openings will normally extend over the entire area of the belt, butshould at least cover a band along said belt as wide as, or slightlywider than, the width of the workpiece. The openings should be arrangedto cover an area somewhat wider than the workpiece if it is desired toreciprocate the workpiece crosswise of the belt during the grindingprocess. The flow of electrolyte through the belt is primarilycontrolled by the openings provided, as hereinafter described, in theplaten behind the belt so that, for commercially acceptable purposes, itis normally preferable to provide openings over the entire surface ofthe belt. The outer surface 22 of the belt19 has a coating ofelectrically nonconductive abrasive material, such as aluminum oxide,silicon carbide or diamond bort, which may be afiixed to said belt inany conventional manner. Itis important that the particles comprisingthe coating extend from the outer surface of the belt not more thanapproximately 0.005 inch, preferably about 0.001 inch, and thatthey doso in a highly uniform man- As a still further alternate, a belt hasbeen satisfactorily made from non-conductive, flexible, material, asfabric, suitably perforated and provided with (a)- electricallyconductive paint on the rearward (against the platen) side and extendingthrough the openings, and (b) suitable bonding-material and abrasivenon-conductive grit onits frontward (adjacent the work). side.

The housing 11 has a relatively fiat platen 26 (FIGURE is parallel withthe inner surface 27 of the frontreach 28' of the belt 19, which reachpreferably moves down wardly. Said platen 26, which may be generallysimilar to the platen shown in Patent No. 2,562,229, has a plurality ofclosely spaced, relatively small openings .29 located in the portion ofsaid platen opposite the grinding position of the workpiece. Saidopenings cover an area slightly wider than the surface of the workpieceengaged by the belt. This area must be somewhat wider if crosswisereciprocation of the workpiece is desired. In a: vertical direction thearea of openings 29 commences at, or slightly above, the lower edge ofthe workpiece and extends somewhat above the upper edge of theworkpiece. The extent of the openings above the upper edge of theworkpiece will depend somewhat. on the freeness ,(rateat which anaqueous liquid can pass through the belt under moderate pressure) of thebelt. In any event the area of openings -will be sufiicient to enablethe electrolyte to' pass through the belt and furnish an adequate supplyof electrolyte to all portions, including the upper portion, of theworkpiece. The openings are of relatively small size in order to effectamore complete and uniform distribution 'of electrolyte being dischargedagainst, and

through, the belt. 7

The platen 26, will preferably be made of any suitable electricallyconductive material, but it should be of suffi cient wear resistentproperties that it will not be unreasonably abraded by the belt.Tungsten carbide is preferable although for a relatively light serviceother types of wear resisting materials or platings can be utilized. Ifthe platen 26 is itself not made of electrically conductive material,then other electrode means will be provided to establish one side of anelectrical potential through electrolyte being expelled through theplatenand belt in the region of the workpiece 47, such as by making thecasing 31 of electrically conductive material, by providing anelectrically conductive terminal within a non-electrically conductivecasing 31 or other convenient means for providing. an electrode incontact with the electrolyte within the casing 31. a

The exact pattern of openings 29 in the area of the platen. occupiedby-said openings may be readily varied as required to fit a givenworkpiece either by replacing the platen 26 as needed or by providingthe openings in a suitable insert 26a removable from the platen.

As shown in FIGURES 3 and 4, a casing 31 of shallow depth is secured tothe rear side of the platen 26 by means, such as the bolts 32, andcombines with the perforate region of the platen 26 to define a smallelectrolyte chamber 33, which communicates with the openings 29. Thechamber -33 is connected by a conduit 34 to a pump 37, which may be ofthe positive displacement type. Said pump 37 has its inlet 38 connectedto a low point in a collecting basin 39 which is disposed beneath andsurrounds the lower pulley 17, as well as the lower portion. of the belt19. The basin 39 extends upwardly and forwardly a suflicient distance tocatch the electrolyte which is moved downwardly from the grinding zoneby gravity and/or the downward movement of the front reach 28.

A work support table- 42 is preferably adjustably supported upon thepedestal 12 bymeans suchas the arm 43 so that its rear edge 44 is closeto but spaced from the front or outer surface 22 of the front reach 28;The worktable 42 is electrically conductive and is connected to one sideofla source 45 of uni-directional electrical energy of either steady orpulsing value and preferably Operation With the grinding machineassembled as shown in FIGURES 1 and 2, it is made ready for use byconnecting the source '45 of electrical energy between the table 42 andadvanced toward the outer surface 22 of 13 and pump 3'7. A workpiece 47is placed upon the table 42 and advanced toward the outer surface 2 2 ofthe front reach 28 of the belt :19 until it is just touching said frontreach 28. The pump 37 causes the electrolyte to flow from the chamber 33through the openings 29 and 21 toward and against the workpiece 47 andfresh electrolyte is constantly supplied thereto partly by direct flowthrough the belt adjacent the workpiece and partly through the beltabove the workpiece from which location it is carried into the grindingzone by the motion of the belt. From the grinding zone the electrolytepartly drops from gravity and partly moves with the belt 19 downwardlyinto the collecting basin 39.

The pump 37 receives the electrolyte collected by the basin 39 and movesit upwardly through the conduit 34 back into the chamber 33 undersufiicient pressure that such electrolyte will again flow through theopenings 29 in the platen 26 and thence through the openings '21 in thebelt 19. The electrolyte thus passing through the belt -19 permits theflow :of current between the workpiece and the platen whereby smallparticles of such workpiece are set free in a known manner byelectrolytic erosion or electrochemical decomposition so that they canbe wiped downwardly by the abrasive coating on the belt 19. it has beenfound that 80 or 90 percent, and sometimes more, of the metal removalfrom the workpiece 47 is effected by the electrolytic erosion and theremaining proportion of metal, and/or products of decompositionotherwise remaining on the work surface, appears to be removed bymechanical action of the abrasive grits constituting the coating. Thus,the primary function of the abrasive coating is :to insulate the belt'19 from direct electrical contact with the workpiece 47 and a secondaryfunction appears to be to wipe off the decomposition products of theelectrical action.

As indicated above, it is essential to the satisfctory operation of thistype of machine that the distance between the outermost conductivesurface of said belt '19 and the workpiece 47 be held to a very smallvalue such as not over 0.005 inch and preferably 0.001 inch, and thatthe flow of electrolyte from the chamber 33 to the adjacent side of theworkpiece 47 receives a minimum of obstruction. Otherwise, the potentialrequired to effect the erosion or decomposition will create anundesirable sensation in the person handling the workpiece 47. With agood electrolyte, which may be any of many known kinds, the potentialprovided by the source 45 can be maintained at less than -10 volts ifthe thickness of the belt 19 and the thickness of the abrasive coatingon said belt are accurate and uniform and within the dimensional limitsset forth above.

Platens and associated structure embodying the invention may becontoured in a wide variety of specific shapes to handle work ofdifierent shapes. For example, as shown in FIGURES 5 and 6, a platen 51having a concave front surface 52 may be provided between the main beltsupporting rollers, such as those shown at 16 and 17 in FIGURE 1. Thefront reach 56 of the grinding belt 57 (FIGURE 6), which my besubstantially identical in construction with the belt 19, may be urgedagainst the front surface 52 of said platen 51 by the workpiece 53 whichis supported upon the table 59. Means, such as the roller shown inbroken lines at 60 in FIGURE 6, may be rotatably mounted upon the table59 for assisting in holding the belt 57 against the platen 5'1.

6 The portion of the platen 5 1 opposite the workpiece has a pluralityof openings 61 (FIGURE 6) which communicate between the openings '62 inthe belt 57 and the chamber 63 behind the central portion of said platen51. Accordingly, by using the alternate platen structure 5'1 it ispossible to produce convex surfaces by means of a belt-ty-pe,electrolytic grinder.

FIGURE 7 illustrates a further alternate platen 66 having a convex outersurface 67 around which the belt 68 extends. A pair of idler rollers 69and 70 may be used if desired to assist in holding the belt in placewith respect to the platen. A guide wheel 72, which is coaxial with, andof a slightly larger radius than, said convex surface 67, may also ifdesired be provided adjacent to the platen 66 and between said rollers69 and '70. The alternate platen has an electrolyte chamber in thecentral portion thereof which communicates with the inlet conduit 71 andwith openings through the outer surface of the platen 66 insubstantially the same manner as set forth with respect to the structureshown in FIG- URE 3. Accordingly, a machine having the alternate platen66 can be used for providing concave surface in a workpiece by theelectr c-chemical decomposition process.

While in each of the embodiments shown the belt is in a verticalposition, and in at least the embodiments of FIGURES 1 to 6, inclusivesome reliance is placed upon gravity to return the electrolyte to thelow pressure side of the pump provided for circulating S81E16, it willbe recognized that the apparatus of the invention may be readilymodified to operate in any other desired position according to thepurposes to be served and reference herein to particular positions willbe understood as used only in connection with the particular embodimenthere chosen to illustrate the invention and not as limiting.

Although particular preferred embodiments of the invention have beendisclosed above in detail for illustrative purposes it will beunderstood that variations or modifications of such disclosure, whichlie within the scope of the appended claim, are fully contemplated.

What is claimed is: A method. of electrolytically grinding a workpieceusing an endless, perforate abrasive belt having nonconductive abrasivegrit thereon, said belt being backed by a perforated platen, whichcomprises:

placing a worlcpiece in touching relationship with the grit on theabrasive belt :which is continuously moved unidirectionally past saidworkpiece so that the Workpiece is spaced a small distance from the beltproper;

continuously circulating an electrolyte through said perforated platenand said belt and against said workpiece, the electrolyte being suppliedthrough the region of the belt contacted by the workpiece and in theregion of the belt above the workpiece so that all portions being groundof the workpiece, including the upper portion, are bathed by theelectrolyte; and

continuously applying a unidirectional electrical potential differencebetween the workpiece as the anode and the electrolyte as it passesthrough said belt.

References Cited in the file of this patent UNITED STATES PATENTS2,526,423 Rudorff Oct. 17, 1950 2,562,229 Bell July 31, 1951 2,722,787Hallewe'll et al. Nov. 8, 1955 2,997,437 Whitaker Aug. 22, 19613,004,910 Keeleric Oct. 17, 1961 3,060,114 Sanders Oct. 23, 19623,099,904 Bell Aug. 6, 1963

